Closed nozzle fuel injectors present specifically defined system dynamics which must be addressed to provide the maximum control possible over the efficiency of the injection event. If the injection event can be terminated quickly, a significant reduction in the amount of fuel delivered to the combustion chamber after injection pressure has dropped below an ideal level can be achieved. This reduction of fuel will measurably reduce exhaust particulates and other products of incomplete combustion.
The prior art has suggested a variety of approaches both to increase the efficiency of the fuel injection event and to improve the longevity and functioning of the fuel injector components. For example, U.S. Pat. No. 4,962,887 to Matsuoka discloses an accumulator fuel injection system which shortens the fuel injection time and increases the fuel injection rate with a control valve that controls accumulator pressure relative to a needle valve closing pressure. It is not suggested, however, that the needle or any of the valve components could be formed of a low inertia or wear-resistant material to have a structure or a mass which will enable an injection event to be more quickly terminated.
U.S. Pat. No. 5,095,872 to Kawamura discloses an engine fuel injection nozzle and needle valve made of a ceramic material. These fuel injection components are designed for use with an engine fueled by alcohol, however, and must be made of a high heat and alcohol-resistant ceramic to optimize combustion of the alcohol and air mixture in the combustion chamber and to avoid overheating of the fuel injection nozzle, although it is suggested that problems with sliding motion are addressed by forming the fuel injection nozzle of ceramic. U.S. Pat. No. 5,076,244 to Donaldson also discloses forming a fuel injection nozzle of a ceramic material. However, an insulating thermal shock resistant ceramic is required for this injector apparatus which is used in an engine fueled by liquified petroleum gas.
U.S. Pat. No. 4,266,729 to Kulke et al. discloses a fuel injection valve with a nozzle needle. An independent needle tip is secured at one end to the nozzle needle, and the other end of the needle tip protrudes through an ejection opening formed within a disc secured to the injector nozzle body. The needle tip and/or the disc are described to be made of corrosion-resistant material, such as high quality steel, ceramic or industrial glass. The use of a corrosion-resistant material to form the needle tip and/or disc is stated to prevent corrosion of these structures and to avoid constriction of the injection opening.
Although the prior art discloses the use of various ceramic components in fuel injector valves, the prior art does not suggest a low inertia, wear-resistant fuel injector valve including a needle valve and spring retainer assembly including ceramic components with a combined mass which improves fuel injector dynamic characteristics. A need exists for such a low inertia, wear-resistant fuel injector valve for a closed nozzle unit fuel injector in a diesel internal combustion engine.